Tag Archives: eyes

Novel glasses can help the color-blind perceive more colors

New research from the UC Davis Eye Center and France’s INSERM Stem Cell and Brain Research Institute could provide glasses that help the color-blind perceive hues.

Image via Pixabay.

As of now, the glasses use “advanced spectral notch filters” to enhance the color-perceiving ability for patients with anomalous trichromacy, the most common type of red-green color vision deficiency (CVD). This effect seemed to persist even after participants took the glasses off, the team adds.

Color-seeing glasses

“Extended usage of these glasses boosts chromatic response in those with anomalous trichromacy (red-green color vision deficiency),” said John Werner, distinguished professor of ophthalmology and a leader in vision science at UC Davis Health, first author of the study.

“We found that sustained use over two weeks not only led to increased chromatic contrast response, but, importantly, these improvements persisted when tested without the filters, thereby demonstrating an adaptive visual response.”

According to the team, 7% of men and 0.5% of women worldwide suffer from CVD — a total of 13 million in the US and 350 million globally. UC Davis, they estimate, has around 1,700 students with red-green CVD.

People with CVD see colors as more muted and washed-out. They have a hard time differentiating between some colors and can perceive a much smaller color palate than an individual with normal color vision.

File:Eight Ishihara charts for testing colour blindness, Europe Wellcome L0059163.jpg
Eight Ishihara charts for testing color blindness, still in use today.
Image credits Medical Photographic Library

The glasses devised by the team use spectral notch filters, which attenuate part of the visible light that hits them. These “EnChroma glasses” should help CVD patients better distinguish colors and make them seem more vibrant and distinct by increasing the separation between different-colored wavelengths of light.

They were given to participants to wear over two weeks. They were asked to keep a diary and were re-tested on days 2, 4, and 11 without wearing the glasses. Another group of students received normal (placebo) glasses.

Individuals with red-green CVD showed a higher ability to distinguish these colors, the team found. This effect persists for some time after wearing the glasses, as revealed by participants’ performance during the re-tests, although it is yet unclear as to how long the effect lasts.

Alex Zbylut, one of the color blind participants in the study, first received the placebo glasses and was then given the experimental ones to try out. He explains that when he goes outside wearing these glasses, “all the colors are extremely vibrant and saturated, and I can look at trees and clearly tell that each tree has a slightly different shade of green compared to the rest. I had no idea how colorful the world is and feel these glasses can help color blind people better navigate color and appreciate the world.”

Werner says this effect can’t be achieved with broad-band filters sold as aids to the color blind. The findings might point to changes in brain networks or processing patterns causing the observed effect — and which may be used as an avenue for treatment in the future.

The paper “Adaptive Changes in Color Vision from Long-Term Filter Usage in Anomalous but Not Normal Trichromacy,” has been published in the journal Current Biology.

404 error.

Your eyes give you away when you’re making a mistake — but only for certain kinds of mistakes

New research at the University of Arizona (UA) is peering into the brain as we make mistakes — and how our eyes give us away.

404 error.

Image credits Andrew Martin.

Pupil size and reactivity correlates with certain types of mistake making, a new paper reports. The findings should help us better understand how our brains react to errors they make, and, possibly, how to make fewer mistakes.

Dilating under error

“When we make decisions in real life, we don’t have all the information presented to us at once; we have to integrate the information over time to make a decision,” said lead author Waitsang Keung, a postdoctoral research associate in the UA Department of Psychology.

“Humans don’t make perfect decisions. They’re subjected to a lot of cognitive biases, so one question is what kind of biases are they subjected to in this process of integrating evidence over time?”

The team worked with 108 participants that they put through an auditory test in the lab. Each participant was asked to listen to a series of 20 clicks, some played in the left ear and some in the right one, over a single second. They were then asked to decide which ear heard the most click. Every participant repeated the task 760 times on average, and the pattern of clicks varied each time.

If 20 clicks per second sound like a lot, it’s because it is. The team intentionally made their task difficult, so as to make mistakes common. All in all, participants got the wrong answer 22% of the time. All through the trials, the participants’ pupils were tracked so the team could see how they behaved when an error was made.

Drawing from this data, the team examined four sources believed to contribute to mistake making in simple (or perceptual) decisions. The first of these sources is that we place different value on parts of information we receive over time. For example, some students participating in a class will give a great deal of weight to the speaker’s opening remarks — known as “primacy effect” — while others will be moved by the final comments instead — the “recency” effect. This pattern of lending different weight to information over time is known as the “integration kernel”, according to the team.

Another cause would be brain ‘noise‘, which is its inability to interpret all input flawlessly. Finally, the team looked at an ‘order effect from previous trials’, which is the tendency for our present decisions to be influenced by past choices and outcomes, as well as ‘irrational side biases’ — these are an individual’s consistent preference for one choice over another, regardless of the evidence they’re faced with.

While the participants made mistakes based on all four of these sources, only two of them correlated with pupil dilation — those caused by brain noise and uneven integration kernels. Participants who weighted evidence more unevenly during the task showed pupil dilation upon making a mistake, particularly those who placed most weight on clicks heard during the middle of the task (rather than at the beginning or end). Uneven integration kernels were the second-leading cause of errors made during the trial, the team adds. Brain noise was the leading cause of errors, and also correlated with pupil dilation upon errors.

“The brain is an intrinsically noisy thing, because it’s basically a computer made of fat and water. It has an intrinsic inability to represent stimuli perfectly,” said UA assistant professor of psychology and paper co-author Robert Wilson.

Mistakes caused by order effect from previous trials or irrational side biases were not correlated with changes in pupil size.

Pupil size is indicative of norepinephrine levels in the brain, the team explains. This neurotransmitter plays a part in arousal modulation, and the team used pupil dilation as a proxy to measure how much of it was in each participant’s system.

“Arousal processes seem to be involved in modulating two kinds of mistakes, but not all four kinds of mistakes, and it may be norepinephrine-driven,” Wilson said. “That potentially means that norepinephrine is controlling the number of mistakes that we’re making and our amount of behavioral variability.”

“We’re really trying to get at this question of why do we make mistakes, and the answer is, in part, because we have multiple systems in our brain that are sort of competing with each other and causing us to make suboptimal decisions. To a certain extent that’s controllable, but not completely.”

The team notes that while some participants showed a strong pupillary response upon making a mistake, others showed a weak response, even none altogether — it all depended on what caused said mistake. That raises the question of why some people are more prone to making a certain kind of mistake than others, but the team says they need to look into the issue in the future. They’re also interested in finding out whether modulating norepinephrine levels in the brain can be used to “control” the number of mistakes we make.

The paper “Regulation of evidence accumulation by pupil-linked arousal processes” has been published in the journal Nature.

The parietal and pineal foramina in the extinct monitor lizard are visible on the overlaid skull. Credit: Senckenberg Gesellschaft für Naturforschung / Andreas Lachmann.

Extinct monitor lizard used to have four eyes — and this is a pretty big deal

Scientists were stunned by the discovery of a four-eyed ancient monitor lizard that went extinct around 34 million years ago. This is the first example of such a creature among jawed vertebrates. To this day, the only animal that we know of that has four eyes is the jawless lamprey.

The parietal and pineal foramina in the extinct monitor lizard are visible on the overlaid skull. Credit: Senckenberg Gesellschaft für Naturforschung / Andreas Lachmann.

The parietal and pineal foramina in the extinct monitor lizard are visible on the overlaid skull. Credit: Senckenberg Gesellschaft für Naturforschung / Andreas Lachmann.

It used to be common among primitive lower vertebrates to have a ‘third eye’, a socket in the skull known as the pineal organ. As with a regular eye, the pineal eye is made up of a cornea, a lens, and a retina. However, unlike conventional eyes that can discern sharp features, a pineal eye is far more limiting, being only able to detect changes in brightness. ‘Now it’s dark; now it’s sunny,’ the third-eye tells the creature. Many existing reptiles such as monitor lizards, some iguanas, and the tuatara still have a pineal eye.

Of course, a pair of eyeballs can also inform a creature whether’s it’s dark or light outside, so what’s the point of having an awesome third eye? Research shows that in reptiles, the pineal eye acts more as a calendar, sensing when days are growing shorter and nights longer, informing the brain of seasonal fluctuations. The third eye may also aid in orientation. Our early pre-mammalian ancestors all had a third-eye, researchers think, but over the course of evolutionary history, it has since been discarded with the pineal organ being incorporated in the endocrine system.

A monitor lizard skull fossil fragment where both the parietal and pineal foramina are visible (highlighted in yellow). Credit: Yale Peabody Museum of Natural History.

A monitor lizard skull fossil fragment where both the parietal and pineal foramina are visible (highlighted in yellow). Credit: Yale Peabody Museum of Natural History.

There’s also a fourth eye-like photosensory structure known as the parapineal organ, and today lampreys form eyes from both structures. But when researchers at the Senckenberg Research Institute in Germany analyzed two specimens of the ancient monitor lizard Saniwa ensiden, which were collected during the 19th century in Wyoming, they were amazed to find that this ancient creature had both pineal and parapineal organs.

The CT scans showed that the individuals had spaces where a fourth eye could have been seated. This suggests that third eye of lizards evolved independently from those in other vertebrate groups. In fact, other researchers are studying third eyes in fossils to come up with a better timeline for the split between ‘cold’ and ‘warm’ blooded of our pre-mammalian ancestors. That’s because all reptiles that still have the pineal eye today are ‘cold-blooded’ while modern mammals, which are all ‘warm-blooded’, lack a pineal eye. Using such an approach, South African researchers at the University of the Witwatersrand estimated that this transition occurred 246 million years ago. 

Scientific reference: Current Biology, Smith et al.: “The Only Known Jawed Vertebrate with Four Eyes and the Bauplan of the Pineal Complex” http://www.cell.com/current-biology/fulltext/S0960-9822(18)30206-9 , DOI: 10.1016/j.cub.2018.02.021.

Insects see in much better resolution than we thought

We may have to re-think what we know about how the little creatures see.

Arthropods such as this Calliphora vomitoria fly have compound eyes. Image credits: JJ Harrison.

Insects see the world much differently from us, that much is clear. For the longest time, researchers thought they are unable to see fine images due to the way their eyes are built. Most insects have compound eyes which consist of many (up to thousands) tiny lens-capped ‘eye-units’. Together, these work to create a low resolution, pixelated image.

Contrasting to that, our own eyes have a single lens, a “megapixel camera” that can actively change the lens shape according to different needs and can keep both nearby and far away objects in sharp focus, based on our different needs. The end result of our eyes is a densely-packed, high-resolution image. Very different from that of insects — or at least that’s what we thought.

Researchers from the University of Sheffield’s Department of Biomedical Science challenge that long-held view. Working with colleagues from Beijing, Cambridge, and Lisbon, they found that insect compound eyes can also generate surprisingly high-resolution images, due to the way the photoreceptor cells deal with image movement.

Unlike the human lens, the insect eyes cannot move to accommodate different images. But the University of Sheffield researchers found that they do something else to compensate for that: underneath the lenses, photoreceptor cells move rapidly in and out of focus as they sample the world around them. This twitch-like movement is so fast that we can’t see it with the naked eye, and has long escaped detection from biologists. In order to thoroughly study it, researchers had to improvise a special microscope.

Researchers conducted in vivo electrophysiological measurements to understand how insects see. Image credits: Mikko Juusola et al — University of Sheffield.

A photoreceptor cell is a specialized type of cell found in the retina that absorbs light (photons). By triggering a change in the cell’s membrane potential, they transform this sensorial input into electrical signals which are then passed on to the brain. Compound eyes are better at detecting edges and are capable of forming images, but were thought to fare worse in terms of overall image quality. They still fare worse than human eyes, it’s just not as bad as we thought.

“By using electrophysiological, optical and behavioural assays with mathematical modelling we have demonstrated that fruit flies (Drosophila) have much better vision than scientists have believed for the past 100 years.”

If these findings are confirmed, then insects combine these normal head/eye movements with super-fast twitching to resolve the world in much finer detail. So far, this improved vision has only been detected in fruit flies (Drosophila), but researchers will soon move on to other insects, as well as vertebrates, in the hope of identifying similar patterns.

Mikko Juusola, Professor of Systems Neuroscience at the University of Sheffield and lead author of the study, said:

“From humans to insects, all animals with good vision, irrespective of their eye shape or design, see the world through fast saccadic eye movements and gaze fixations.It has long been known that fast visual adaptation results in the world around us fading from perception unless we move our eyes to cancel this effect. On the other hand, fast eye movements should blur vision which is why it has remained an enigma how photoreceptors work with eye movements to see the world clearly.”

“Our results show that by adapting the way photoreceptor cells sample light information to saccadic eye movements and gaze fixations, evolution has optimised the visual perception of animals. ”

The findings have been published in the open-access journal eLife.

Scientists find a woman that can see 99 million more colors than you or me

Neuroscientists in the UK have recently announced that their 25 year long search for a tetracromath — a person with an extra type of cone cell in his or her retina — has finally come to a successful end. They estimate that the woman can see a staggering 99 million more colors than other humans, and they believe there are many more people like her waiting to be discovered.

Image via pixabay

Our eyes‘ retina house cone cells that can distinguish color variation in incoming light. Humans usually have three types of cone cells, each able to detect the presence of a single color — green, red, or blue — and are thus known as “trichromats.” Most color blind people and most other mammals only have two different types of cone cells, and are “bichromats.” As each cell can distinguish between 100 or so shades of the same color, each extra type of cone cell increases the number of colors we can see exponentially. So where a color blind person can see around 10,000 shades, a healthy human can see around 1 million different colors.

But what if human beings had not three, but four types of cone cells in their retinas? That would allow a person to see 100 million colors — colors most of us have never even dreamed of, colors we have no way of even imagining. The existence of such people, or “tetrachromats,” was first proposed in 1948 by Henri Lucien de Vries, a Dutch scientist researching with color blind patients. He found that while his male subjects had two types of normal cone cells and one mutant type that was less sensitive and didn’t pick up on its corresponding color (either green or red,) the female subjects had three normal cone cell types and one mutant type. Even if this extra type of cell didn’t actually do anything, it suggested that humans can have more than three types of cells.

Interest in tetrachromats largely died out until the late ’80s, when Professor John Mollon from Cambridge University started looking for women who might have four functioning cone cell types. He estimated that, if color blind men could pass this fourth cell type to their daughters, around 12% of the female population should be tetrachomats. However, he never actually found a person with four different fully functional types of cone cells, a tetrachromat.

But now, 25 years after they’ve first started searching, UK scientists believe they’ve finally found such a woman. Known as cDa29, she was identified by Newscastle University neuroscientist Gabriele Jordan, a former coleague of Mollon, after she decided to use a different test than those the professor employed in his search.

She took 25 women who had a fourth type of cone cell, and put them in a dark room. Looking into a light device, three colored circles of light flashed before these women’s eyes. To you and me the circles would look the same, but Jordan believed that a true tetrachromat could tell them apart, as the fourth type of cone cells would allow her to pick up on the subtle differences.

One of the women tested, cDa29, was able to differentiate the three different colored circles on every single try.

“I was jumping up and down,” Jordan told Discover magazine.

But why did it take so long to find a tetracromat if there’s so many of them? One issue is that the team only carried out their search in the UK. But more importantly, Jordan says, is that most true tetrachromats simply don’t know they’re any different from the rest of us.

“We now know tetrachromacy exists,” she said. “But we don’t know what allows someone to become functionally tetrachromatic, when most four-coned women aren’t.”

Jay Neitz, a vision researcher at the University of Washington, who wasn’t involved in the study, thinks that tetrachromats simply haven’t had a chance to use their eyes to their full potential in our society.

“Most of the things that we see as coloured are manufactured by people who are trying to make colours that work for trichromats,” he said. “It could be that our whole world is tuned to the world of the trichromat.”

The research on cDa29 hasn’t been peer-reviewed or published as yet, and Jordan is continuing her research and search for more tetrachromats. Her results still need to be verified but if tetrachromats really do exist, it could teach us a lot about how vision works.

One thing we might never be able to understand, however, is exactly what the world looks like through cDa29’s eyes.

“This private perception is what everybody is curious about,” Jordan told Discover. “I would love to see that.”

Researchers coax neurons into regenerating and restore vision in mice

Stanford University researchers have developed a method that allows them to regrow and form connections between neurons involved in vision. The method has been only tested on mice but the results suggest that mammalian brain cells can be restored after being damaged — meaning maladies including glaucoma, Alzheimer’s disease, and spinal cord injuries might be more repairable than has long been believed.

Neurons are the building blocks of our nervous system.
Image via youtube

It has long been believed that mammalian brain cells can’t regrow, but the new study shows that it’s possible. The team reports that they’ve managed to regenerate the axons of retinal ganglion cells, and although fewer than 5 percent of cells responded to the method, it was enough to make a difference in the mice’s vision.

“The brain is very good at coping with deprived inputs,” says Andrew Huberman, the Stanford neurobiologist who led the work. “The study also supports the idea that we may not need to regenerate every neuron in a system to get meaningful recovery.”

“I think it’s a significant step forward toward getting to the point where we really can regenerate optic nerves,” says Johns Hopkins professor of ophthalmology Don Zack, who was not involved in the research. “[It is] one more indication that it may be possible to bring that ability back in humans.”

The study shows that a regenerating axon can grow in the right direction, forming the connections needed to restore function.

“They can essentially remember their developmental history and find their way home,” Huberman says. “This has been the next major milestone in the field of neural regeneration.”

Once central nervous system cells reach maturity, they flip a genetic switch and never grow again. The team used genetic manipulation to flip this switch back on, activating the so-called “mammalian target of rapamycin” (mTOR) signaling pathway, which helps stimulate growth. At the same time, they exercised the damaged eye by showing mice a display of moving, high-contrast stripes.

“When we combined those two [methods]—molecular chicanery with electrical activity—we saw this incredible synergistic effect,” Huberman says. “The neurons grew enormous distances—500 times longer and faster than they would ordinarily.”

They observed that by covering the mice’s good eyes so they looked at the stripes only with their damaged eyes, the neurons regenerated faster. The team used a virus to deliver the altered genes to their mice, but study co-author Zhigang He believes there may be simpler ways to achieve this, such as pills, for human treatment. He, who developed the mTOR procedure, isn’t sure how the findings will impact human patients. He notes that a dual procedure, similar to that they used for the rats, hasn’t yet been developed for humans. He also pointed out that our retinal cells would have to grow a lot more than a mouse’s to rewire vision.

“The human optic nerve has to regenerate not on the scale of millimeters but on the scale of centimeters,” he explains.

Further research is needed to figure out the best use of this method for patients.

“Before, there was nothing to do” about damage to retinal nerves or other brain cells, says He, whose lab studies both retinal and spinal cord damage. “Now, we need to think about what type of patient might be most likely to benefit from the treatment.”

Huberman hopes that his method will be usable within a few years to help patients with early-stage glaucoma avoid the degeneration that leads to blindness.

“There are going to be many, many cases in which glaucoma could be potentially treated by enhancing the neural activity of retinal ganglion cells,” he says.

The findings also suggest that other brain cells could be determined to self-repair, Huberman says. Potential applications include restoring some movement after spinal cord damage, fighting memory-related diseases such as Alzheimer’s and even helping patients manage the symptoms of autism.

The full paper, titled “Neural activity promotes long-distance, target-specific regeneration of adult retinal axons” has been published in the journal Nature Neuroscience.

Dark circles around eyes

Why we get dark circles around the eyes

Dark circles around eyes

Credit: Flickr user Anna Gutermuth

Dark circles under the eyes or periorbital dark circles, as they’re referred to in medicine, are a sign of fatigue. Some people, however, have these dark circles despite having a good night’s sleep — that’s simply the way they are, and not a cause for concern if it’s hereditary.

These periorbital dark circles are very conspicuous because the skin around the eyes is the thinnest in all the body, around four times thinner than the rest of the body to be more precise.

Since the skin can become so thin, blood vessels are easily seen. This is why a bruise around the eyes shows worse than any other place on the body — you can just see more easily the ruptured blood vessels through the thin skin.

It’s the blood that makes dark circles appear blue, most of the time. Even though blood isn’t blue, the skin only allows violet wavelengths of light to pass through, so only blue light is reflected back to hit retinas, making veins look bluish. People with darker skin tend to have veins which appear green or brown. As an oddity, people with very light skin, such as albinos, will have dark circles that appear dark red or dark purple, which more closely resembles the color of blood.

As we age, skin becomes thinner all over the body and loses elasticity, areas around the eyes included. This is why the elderly have prominent periorbital dark circles, even though they’re well rested. Jokingly or not, many say about the elderly that they’ve become tired by living such a long life, which is true to a certain extent but not in the way they think.

Some people are genetically predisposed to have dark circles all the time, young or old, because of a condition known as periorbital hyperpigmentation. The condition causes the skin below the eyes to produce more melanin —  the pigment that gives human skin, hair, and eyes their color — resulting in it appearing darker.

Periorbital hyperpigmentation doesn’t pose any medical risks, “however the development of dark circles under the eyes in any age is of great aesthetic concern because it may depict the individual as sad, tired, stressed, and old,” wrote dermatologist Roberts WE. He says the condition (which mostly affects people with darker skin) is challenging to treat, complex in pathogenesis, and lacking straightforward and repeatable therapeutic options, which is why many turn to cosmetics to cover up the skin around the eyes.

Other conditions that may cause dark circles:

  • Allergies
  • Nasal congestion
  • Medical conditions (eczema, thyroid problems, etc.)
  • Venous congestion in under eye blood vessels
  • Environmental exposure
  • Heredity

Lifestyle choices can also lead to prominent dark circles around the eyes. These may include:

  • Smoking
  • Hyperpigmentation caused by sun damage
  • Caffeine consumption
  • Alcohol consumption
  • Sleep deprivation
  • Dehydration
  • Dietary deficiencies

Bilateral periorbital ecchymosis (raccoon eyes). Credit: Wikimedia Commons

Bilateral periorbital ecchymosis (raccoon eyes). Credit: Wikimedia Commons

Raccoon eyes

Hand in hand with preorbital dark circles is periorbital puffiness, or saggy bags below the eyes. Allergies, excessive salt consumption, and diseases like the flu cause fluid to build up below the eyes. The saggy bags exert more pressure on the skin and blood vessels which surround the eyes making dark circles appear even more prominent. That’s for young people. As with dark circles, many old people get periorbital puffiness no matter what.

Nothing comes close, however, to periorbital ecchymosis, also known as “raccoon eyes” or “panda eyes”. This condition typically occurs when a person suffers a nasty blow to the head, and the resulting skull fracture or ruptured meninges causes blood to flood the soft tissue around the eyes. Sometimes cancer may be involved. Raccoon eyes are serious business and require urgent medical attention which often leads to surgery.

Half the world will need glasses by 2050

Nearly half the world’s population, close to some 5 billion people, will develop myopia by 2050 according to a study recently published in the journal Ophthalmology. The paper also estimates that one-fifth of these people will have a significantly increased risk of becoming permanently blind from the condition if recent trends continue.

"Can you come a bit closer? I can't see you yet." Image via flikr @ Paul Stevenson.

“Can you come a bit closer? I can’t see you yet.”
Image via flikr @ Paul Stevenson.

The number of myopia cases is rapidly rising across the globe, making it one of the most common sight-impairment conditions of the modern world. This increase is attributed to “environmental factors (nurture), principally lifestyle changes resulting from a combination of decreased time outdoors and increased near work activities, among other factors,” according to a new study from Brien Holden Vision Institute, University of New South Wales Australia and Singapore Eye Research Institute.

Even worse, if the current trends continue, the paper warns that we’ll see a seven-fold increase in cases from 2000 to 2050. Myopia will also become one of the leading causes of permanent blindness by that date.

But why? Short-sightedness has always been around but never at the scale this study predicts.

It’s mostly due to the way we use our eyes today. For most purposes, our eyes are good at spotting far away objects, but they have been mostly relegated to short distance duty nowadays. Our daily activities involve a lot of “near work activities,” such as using a computer, scrolling on a smartphone or reading. Constantly keeping focus on a short distance leaves the crystalline lens in our eyes set on them, in a sense, and unable to effectively focus on objects farther away.

The authors point out that this has become a major public health issue, one that we’ll have to tackle — preferably sooner rather than later. They suggest that planning for comprehensive eye care services is needed to manage the rapid increase in high myopes (a five-fold increase from 2000), along with the development of treatments to control the progression of myopia and prevent people from becoming highly myopic.

“We also need to ensure our children receive a regular eye examination from an optometrist or ophthalmologist, preferably each year, so that preventative strategies can be employed if they are at risk,” said co-author Professor Kovin Naidoo, CEO of Brien Holden Vision Institute. “These strategies may include increased time outdoors and reduced time spent on near based activities including electronic devices that require constant focussing up close.

“Furthermore there are other options such as specially designed spectacle lenses and contact lenses or drug interventions but increased investment in research is needed to improve the efficacy and access of such interventions.”

Yea so….I’d say investing in the glasses industry will probably net you a nice return in a few years.

But there is an upside to this paper. Don’t want myopia? Drop your laptop and spend some time in the park. Put your smartphone in your pocket and look at the city as you walk to work or school. You might even end up having fun.

The full paper, titled “Global Prevalence of Myopia and High Myopia and Temporal Trends from 2000 through 2050” is available online in the journal Ophthalmology here.

 

How the eye works

 

Image via flickr. 

Doing some light reading

Touch interprets changes of pressure, texture and heat in the objects we come in contact with. Hearing picks up on pressure waves, and taste and smell read chemical markers. Sight is the only sense that allows us to make heads and tails of some of the electromagnetic waves that zip all around us — in other words, seeing requires light.

Apart from fire (and other incandescent materials), bioluminiscent sources and man-made objects (such as the screen you’re reading this on) our environment generally doesn’t emit light for our eyes to pick up on. Instead, objects become visible when part of the light from other sources reflects off of them.

Let’s take an apple tree as an example. Light travels in a (relatively) straight line from the sun to the tree, where different wavelengths are absorbed by the leaves, bark and apples themselves. What isn’t absorbed bounces back and is met with the first layer of our eyes, the thin surface of liquid tears that protects and lubricates the organ. Under it lies the cornea, a thin sheet of innervated transparent cells.

Behind them, there’s a body of liquid named the aqueous humor. This clear fluid keeps a constant pressure applied to the cornea so it doesn’t wrinkle and maintains its shape. This is a pretty important role, as that layer provides two-thirds of the eye’s optical power.

Anatomy of the eye.
Image via flikr

The light is then directed through the pupil. No, there’s no schoolkids in your eye; the pupil is the central, circular opening of the iris, the pretty-colored part of our eyes. The iris contracts or relaxes to allow an optimal amount of light to enter deeper into our eyes. Without it working to regulate exposure our eyes would be burned when it got bright and would struggle to see anything when it got dark.

The final part of our eye’s focusing mechanism is called the crystalline lens. It only has half the focusing power of the cornea but its most important function is that it can change how it does this. The crystalline is attached to a ring of fibrous tissue on its equator, that pull on the lens to change its shape (a process known as accommodation), allowing the eye to focus on objects at various distances.

Fun fact: You can actually observe how the lens changes shape. Looking at your monitor, hold your up hands some 5-10 centimeters (2-4 inches) in front of your eyes and look at them till the count of ten. Then put them down; those blurry images during the first few moments and the weird feeling you get in your eyes are the crystalline stretching to adapt to the different focal vision.
Science at its finest.

After going through the lens, light passes through a second (but more jello-like) body of fluid and falls on an area known as the retina. The retina lines the back of the eye and is the area that actually processes the light. There are a lot of different parts of the retina working together to keep our sight crispy clear, but three of them are important in understanding how we see.

  • First, the macula. This is the “bull’s eye” of the retina. At the center of the macula there’s a slight dip named the fovea centralis (fovea is latin for pit). As it lies at the focal point of the eye, the fovea is jam-packed with light sensitive nerve endings called photoreceptors.
  • Photoreceptors. These differentiate in two categories: rods and cones. They’re structurally and functionally different, but both serve to encode light as electro-chemical signals.
  • Retinal pigment epithelium. The REP is a layer of dark tissue whose cells absorb excess light to improve the accuracy of our photoreceptors’ readings. It also delivers nutrients to and clears waste from the retina’s cells.

So far you’ve learned about the internal structure of your eyes, how they capture electromagnetic light, focus it and translate it into electro-chemical signals. They’re wonderfully complex systems, and you have two of them. Enjoy!

There’s still something I have to tell you about seeing, however. Don’t be alarmed but….

The images are all in your head

While eyes focus and encode light into the electrical signals our nervous system uses to communicate, they don’t see per se. Information is carried by the optical nerves to the back of the brain for processing and interpretation. This all takes place in an area of our brain known as the visual cortex.

Brain shown from the side, facing left. Above: view from outside, below: cut through the middle. Orange = Brodmann area 17 (primary visual cortex)
Image via wikipedia

Because they’re wedged in your skull a short distance apart from each other, each of your eyes feeds a slightly different picture to your brain. These little discrepancies are deliberate; by comparing the two, the brain can tell how far an object is. This is the mechanism that ‘magic eye’ or autostereogram pictures attempt to trick, causing 2D images to appear three dimensional.  Other clues like shadows, textures and prior knowledge also help us to judge depth and distance.

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The neurons work together to reconstruct the image based on the raw information the eyes feed them. Many of these cells respond specifically to edges orientated in a certain direction. From here, the brain builds up the shape of an object. Information about color and shading are also used as further clues to compare what we’re seeing with the data stored in our memory to understand what we’re looking at. Objects are recognized mostly by their edges, and faces by their surface features.

Brain damage can lead to conditions that impair object recognition (an inability to recognize the objects one is seeing) such as agnosia.  A man suffering from agnosia was asked to look at a rose and described it as ‘about six inches in length, a convoluted red form with a linear green attachment’. He described a glove as ‘a continuous surface infolded on itself, it appears to have five outpouchings’. His brain had lost its ability to either name the objects he was seeing or recognize what they were used for, even though he knew what a rose or a glove was. Occasionally, agnosia is limited to failure to recognize faces or an inability to comprehend spoken words despite intact hearing, speech production and reading ability.

The brain also handles recognition of movement in images. Akinetopsia, a movement-recognition impairing condition is caused by lesions in the posterior side of the visual cortex. People suffering from it stop seeing objects as moving, even though their sight is otherwise normal. One woman, who suffered such damage following a stroke, described that when she poured a cup of tea the liquid appeared frozen in mid-air, like ice. When walking down the street, she saw cars and trams change position, but not actually move.

Looking into someone’s eyes for 10 minutes alters your state of mind and can cause hallucinations

Staring straight into someone’s eyes can be pretty intense, and is usually avoided by most people. But a team of researchers has shown that it’s even more intense than you’d think: it actually alters your consciousness, and often causes hallucinations.

Image via Imgneed.

This particular study was conducted on only 20 volunteers, but the results were consistent across all participants. They weren’t told what the purpose of the study was, only knowing that it had to do with a “meditative experience with eyes open”. They were placed in pairs of 2 in a dimly lit room and asked to look at their partner’s eyes for 10 minutes straight. After that, they were asked to complete questionnaires related to what they experienced during and after the experiment.

Not only did the experiment bring on strange ‘out of body’ experiences for the volunteers, it also caused them to see hallucinations of monsters, their relatives, and themselves in their partner’s face. Quite a strange trip, for only looking into someone’s eyes.

“The participants in the eye-staring group said they’d had a compelling experience unlike anything they’d felt before,” Christian Jarrett writes for the British Psychological Society’s Research Digest. 

Scientists aren’t sure what it is, but something about starting into human eyes seems to bring out these strange reactions.

Jarrett explains:

“On the dissociative states test, they gave the strongest ratings to items related to reduced colour intensity, sounds seeming quieter or louder than expected, becoming spaced out, and time seeming to drag on. On the strange-face questionnaire, 90 percent of the eye-staring group agreed that they’d seen some deformed facial traits, 75 percent said they’d seen a monster, 50 percent said they saw aspects of their own face in their partner’s face, and 15 percent said they’d seen a relative’s face.”

The results are consistent with another, 2010 study, in which participants were asked to look at their reflection in a mirror for 10 minutes, focusing on the eyes. The paper, entitled Strange-Face-in-the-Mirror Illusion, reports that after less than a minute, the volunteers started seeing illusions and experiencing strange emotions.

“The participants’ descriptions included huge deformations of their own faces; seeing the faces of alive or deceased parents; archetypal faces such as an old woman, child or the portrait of an ancestor; animal faces such as a cat, pig or lion; and even fantastical and monstrous beings,” Susana Martinez-Conde and Stephen L. Macknik write for Scientific American. “All 50 participants reported feelings of ‘otherness’ when confronted with a face that seemed suddenly unfamiliar. Some felt powerful emotions.”

Although in all fairness, it may have nothing to do with eyes at all. This phenomenon might be caused by neural adaptation – in other words, if you’re continuously looking at the same thing, your neurons become less and less stimulated, the perception starts to fade, and you start to see other things where other things simply aren’t.

(c) Nickolay Lamm

How cats see the world (with pictures)

As a cat owner myself, I’ve often wondered how feline vision differs from that of humans. Clearly, with their huge pupils and crocodile-like eyes, their view of the world must be truly different from ours. Artist Nickolay Lamm recently showcased a project that features various photos from two points of view: the human and the cat. While not the most realistic take on how cats see, these photos offer an interesting glimpse on how felines see.

(c) Nickolay Lamm

(c) Nickolay Lamm

To alter his photographs in a way similar to how a cat would see, Lamm consulted with ophthalmologists at the University of Pennsylvania’s veterinary school and a few other animal eye specialists. For each photo, the top view is an unfiltered photograph that portrays what we humans normally see, while the bottom view shows the same photo from the cat’s perspective.

(c) Nickolay Lamm

(c) Nickolay Lamm

You might notice that cat vision is much more blurry than ours. Cat’s see really well in the dark, but for this, they had to sacrifice fine details and some colours to be able to see well in low-light conditions. Also, notice that the cat’s vision is slightly broader than ours.  That’s because cats see 200 degrees compared to our 180 degrees.

(c) Nickolay Lamm

(c) Nickolay Lamm

Cats don’t see very well at a distance. While human vision is perfectly adapted for seeing sharply 100 feet away, cats barely can distinguish fine details past 20 feet. Apparently, kitties miss out on the beauties of foreground landscapes.

Nickolay Lamm

(c) Nickolay Lamm

But no matter, kitties are fine with seeing in the dark. Cat eyes have much more rods than humans – photoreceptor cells in the retina – which allows them to absorb more light and see better in low-light conditions. Their elliptical pupils can open very wide in dim light, but contract to a tiny slit to protect the sensitive retina from bright light.  Ever took a picture of a cat only to see afterward that it looked like the spawn of Satan, with fire blazing from its eyes? This Terminator-feel happens because cats have what’s called an atapetum lucidum – a reflective layer that bounces light that hits the back of the eye out through the retina again for a second chance to be absorbed by the rods, which allows them to see even better at night.

via PopSci

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Delusion

Delusional people actually see the world differently

There’s an extremely fine line between delusion and grand vision – it’s enough just to take a look back in history and you’ll find a myriad of examples where great minds who justly challenged the status quo were labeled insane, and in some even more unfortunate times, heretics. That’s not to say that behind every conspiracy theorist or person who emits extreme, upside-down hypotheses lies on man of genius or great foreseeing. Much of the time, these are truly simple delusions – erroneous views on the world and how it works. A new study addressed how delusions work and how people who have them ‘see’ the world. The findings are most interesting: according to researchers at Yale University in New Haven, Conn, the delusional mind actually perceives the world in a manner different from what  most would class as real.

“Beliefs form in order to minimize our surprise about the world,” said neuroscientist Phil Corlett of Yale University in New Haven, Conn., who was not involved in the study. “Our expectations override what we actually see,” Corlett added.

DelusionIn other words, our beliefs are guided and formed by our perception. If we perceive something – an event, a concept, even a way of life – differently than our minds predicted it should be, then we generally change/update our belief. What we see or what we understand of certain events is extremely subjective, and some folks are prone to forming delusions. The Yale University researchers found that people who form delusions typically do not distinguish correctly among different sensory inputs.

This is why some people suffer from extreme cases of paranoia, constantly feeling they’re being watched or persecuted. Others have inflated ideas about one’s selves, believing they’re  in much greater position than they actually are. Nevertheless, the researchers conducted a series of experiments to test how delusions form and how these work in the brain.

Seeing the world though different eyes

First off healthy volunteers, with no mental health problems, were recruited and asked to fill in a questionnaire that measured how delusional they were. Questions included: “do you ever feel as if people are reading your mind?” “Do you feel there’s a conspiracy against you?” and even “Do you feel like your partner may be unfaithful?”.

Next, the study participants were asked to perform a task that tested their visual perception. A sphere-like set of dots would rotate in an ambiguous direction, and participants had to report which direction they perceived the dots were heading towards at various intervals. People who scored high on the questionnaires  saw the dots appear to change direction more often than the average person, suggesting what other similar studies had already found as well: delusional individuals have less stable perceptions of the world.

In a second experiment, participants were offered ‘special glasses’ which they were told would bias their view so that the rotating dots would appear to go in one direction more often than the other direction. This was simple trolling the scientists’ part, if you will, since these were nothing but ordinary glasses. The same experiment as in the first part was played, but in two phases: in the learning phase, where dots clearly rotated in one direction and a test phase, where the direction was ambiguous.

The participants reported they were seeing the dots rotate in the biased direction even in the test phase, when clearly didn’t happened. They clung to the delusion that the glasses altered their vision, even though the visual evidence contradicted this idea, suggesting they used their delusional beliefs to interpret what they were seeing.

In a third try, the same experiment was once again repeated but this time participants had brain scans done on them using fMRI. Brain imaging revealed that as people were deluded about the direction of the dots’ rotation, their brains were encoding the delusion as if they had really seen the dots move that way. Otherwise said, these people weren’t ignoring or actively denying what they saw – they were genuinely seeing/perceiving something else. Scans also revealed links between a brain area involved in beliefs, the orbitofrontal cortex, and an area involved in visual processing, the visual cortex.

via Live Science

New theory claims Neanderthals went extinct due to larger eyes

Apparently, every month brings forth a new theory on the demise of the Neanderthals – the cookies one being that bunnies were the main culprit. This month’s theory claims that the Neanderthal skull has larger eye sockets than the human one, therefore it had bigger eyes, therefore the brain spent more of its processing power to process visual images.

neanderthal2

So the conclusion is that while we used our brains to deveop clothers and slowly figure out the world we were living in, their brains were more focused on image processing.

The research team explored the idea that the ancestor of Neanderthals left Africa and had to adapt to the longer, darker nights and murkier days of Europe. The result was that Neanderthals evolved larger eyes. Meanwhile, people who were still living in Africa enjoyed bright, beautiful days, and had no need to adapt to hunting in darker conditions.

“Since Neanderthals evolved at higher latitudes, more of the Neanderthal brain would have been dedicated to vision and body control, leaving less brain to deal with other functions like social networking,” she explained.

Apparently, this idea has received a fair amount of support. Prof Chris Stringer, who was also involved in the research and is an expert in human origins at the Natural History Museum in London adds:

“We infer that Neanderthals had a smaller cognitive part of the brain and this would have limited them, including their ability to form larger groups. If you live in a larger group, you need a larger brain in order to process all those extra relationships,” he explained.

neanderthal

According to them, even small differences could provide Homo sapiens the edge over their evolutionary cousins. Neanderthals were very smart and adaptable, but they laked the edge when compared to our species.

“They were very, very smart, but not quite in the same league as Homo sapiens,” he said. “That difference might have been enough to tip the balance when things were beginning to get tough at the end of the last ice age,” he said.

Via BBC

An eye growing on the tail of a tadpole.

Tadpoles can see through eyes implanted in their tails

An eye growing on the tail of a tadpole.

An eye growing on the tail of a tadpole.

Most animals have eyes in the vicinity of their brains, typically inside the head, since these are very sensible organs that require a very sophisticated neural link. Recently, biologists at Tufts University have shown that they could implant working eyes in other locations as well, after they granted blind tadpoles vision after they implanted eyes in their tails. The findings might offer further insight into artificial visions and regenerative medicine.

The scientists experimented with 134 tadpoles of the African clawed frog Xenopus laevis, a popular lab pet for researchers worldwide. These had their eyes surgically removed, after which the scientists painstakingly implanted eyes in their torsos and tails.

An experimental set-up was devised with quadrants of water illuminated by either red or blue LED light. The arena, half illuminated in red, half illuminated in blue, would regularly switch between colors via software. The trick lied in the fact that whenever tadpoles when enter the red district, they would receive a mild electrical shock. A motion-tracking camera kept tabs on where the tadpoles were at all times.

Remarkably, it was observed that six of the tadpoles always kept away from the red half of the arena, hinting that they could see with the eyes implanted in their tails. These eyes came from other genetically engineered tadpoles that were instructed to grow a red florescent protein. This allowed the researchers to see whether the eyes sent red nerves outward in the body. Half the 134 recipient tadpoles had no such nerves grow, while about a quarter had nerves projecting toward the gut and the other quarter had nerves extending toward their spine. All of the six tadpoles that showed signs of vision had nerves plugged into their spine, meaning their new eyes were now linked to their nervous system.

“One of the things that this study showed us is that connecting a sense organ as complex as the eye to the spinal cord is sufficient to confer vision,” Dr. Michael Levin said. “So you don’t have to plug in to the actual brain.”

Does this mean that the tadpoles can see just as well as they used to with their original eyes? In reply to this vexing questions, the scientists’ answer is straightforward – they don’t know. “We have no idea what a tadpole is experiencing. This is a philosophical question that is not immediately tractable,” the researchers write in their paper published in the Journal of Experimental Biology.

It’s well worth noting that applications for this kind of research aren’t limited to regenerative medicine only, augmented technology for instance would have a lot to benefit.

“You may want to increase your sensory capacity with sensors that normal people usually don’t have,” he said. “This opens the possibility for attaching all sorts of peripherals to your body.”

Robot designers could also learn a thing or two from the findings, in terms of adaptive flexibility.

“You can imagine that information that comes from any sensory structure – any part of the body – is tagged in some way that uses a unique identifier,” said Dr. Douglas Blackiston, a post-doctoral associate. “So, the source of that information is not nearly as important as what the brain is sensing.”

human eye evolution

Vision first evolved 700 million years ago

human eye evolutionThe origins of vision is a widely debated subject, since genetic relationships between early animals capable of sight are inconsistent. A team of researchers has conducted an extensive computer analysis that tests every proposed hypothesis on the origin of vision to date, and found a common ancestor dating from 700 million years ago. Their findings suggest vision evolved much earlier than previously thought.

Opsin is photosensitive protein which holds the key to developing optical vision. These vital components trap light in the eyes’ pigments, however when they first evolved has been always a puzzling question for scientists.

Dr Davide Pisani of Bristol’s Schools of Biological Sciences and Earth Sciences and colleagues at NUI Maynooth performed a computational analysis of all available genomic information from all relevant animal lineages, including a newly sequenced group of sponges (Oscarella carmela) and the Cnidarians, a group of animals thought to have possessed the world’s earliest eyes.

With this data at hand, the researchers were able to construct an evolutionary timeline of opsin, which eventually lead them to the point of origin – a common ancestors  to all groups appearing some 700 million years ago. The first opsin originated from the duplication of the common ancestor of the melatonin and opsin genes in a eumetazoan (Placozoa plus Neuralia) ancestor, and an inference of its amino acid sequence suggests that this protein might not have been light-sensitive.

Despite being consider blind, the opsin protein underwent key genetic changes over the span of 11 million years that conveyed the ability to detect light.

“The great relevance of our study is that we traced the earliest origin of vision and we found that it originated only once in animals,” says Dr Davide Pisani.

“This is an astonishing discovery, because it implies that our study uncovered, in consequence, how and when vision evolved in humans.”

Findings were published in the journal PNAS.  Below you can find a very interesting infographic published by Voltier Creative which explains how eyes evolved.

Eye Infographic

weightlessness

Astronauts’ vision severely affected during long space missions

weightlessness

(c) NASA

After the International Space Station was completed, scientists noticed that exposure to weightlessness may have some deleterious effects on human health. The human body is too adjusted to the gravitational conditions on Earth, so extended periods of weightlessness can cause various physiological systems to change and atrophy.

Astronauts on-board the International Space Station battle nausea and vertigo, as well as daily headaches. However, their biggest problem is muscle atrophy, forcing them to exercise constantly to diminish some of the effects.

Another serious weightlessness physiological symptom that is often overlooked is vision deterioration. Previous NASA surveys that interviewed over 300 astronauts post-prolonged space missions (more than six months) revealed that half of all astronauts involved in orbital missions since 1989 complained about changes in near- and far-sightedness. One of 4 astronauts who flew missions of less than 6 months also reported eye problems.

Older crew members, aged over 40, are more predisposed to vision deficiencies, which first start after around six weeks of weightlessness exposure, and go on to continue even months after returning back to Earth. NASA has been aware of this problem for decades now, and for the past few years, it has even issued reading glasses, along with sunglasses, to all of the astronauts that serve long-term space missions.

Recently, the National Aeronautics and Space Administration performed a more in-depth examination of this serious hazard, as the agency conducted a clinical evaluation that involved studying seven astronauts, all of whom were aged around 50 and had spent at least six continuous months in space.

Five of the 7 astronauts in the study complained of lost visual acuity beginning several months into their long-duration flights, and all 7 showed evidence of pathological processes undercutting their vision after their missions. Several abnormalities have been revealed, including the flattening of the back of the eyeball, folds in the vascular tissue behind the retina, and excess fluid around and presumed swelling of the optic nerve.

“If the choroid gets damaged, you may get insufficient or altered blood flow to the photoreceptors, leading to detachment of the retina, leakage of fluid under the retina, or damage to the visual cells,” said Michael F. Marmor, MD, professor of ophthalmology at the Stanford University School of Medicine in California, who was not involved with the study.

The results are currently impacting plans for long-duration manned space voyages, such as a trip to Mars, explained the team including ophthalmologists Dr. Thomas H Mader, of Alaska Native Medical Center, and Dr. Andrew G Lee, of The Methodist Hospital, in Houston, Texas. Their findings have been reported in the October issue of Ophthalmology. 

NASA is constantly developing technology, aided by data provided by studies such as the present one, in order to counter the various worrisome effects zero gravity has on the human body. Regarding vision deficiencies, in particular, astronauts are now required to routinely undergo pre- and post-flight magnetic resonance imaging of their head and eyes, along with dilated fundus exams with photography of the macula and optic nerve, to provide intraocular pressures measurements.

“It is just a question of getting more data,” Dr. Mader said. “Recent long-duration missions have made these changes more pronounced, and improved technologies have served to better analyze these findings.”

Until artificial gravity can finally become functional, astronauts will have to pay for the best views in their lives.